<p>Set the <code>points</code> attribute of the <code>&lt;polygon&gt;</code> or <code>&lt;polyline&gt;</code> subelement relatively to the dimensions and position of the element referenced by the selector in the <code>ref</code> attribute. The <code>refPoints</code> are scaled so that the subelement's dimensions match the reference element's dimensions, and translated so that the their origin matches the origin of the reference element.</p>
<p>The original points offset is preserved. This means that if the top-left corner of the <code>refPoints</code> bounding box does not lie at <code>0,0</code>, the gap between the points and origin is preserved in the rendered shape, as well.</p>

<pre><code>var Polygon = joint.dia.Element.define('examples.Polygon', {
    attrs: {
        polygon: {
            refPoints: '10,10 30,10 30,30', // points offset is 10,10
            fill: 'red',
            stroke: 'black'
        }
    }
}, {
    markup: 'polygon'
});

var p = (new Polygon()).resize(40, 40).addTo(graph);
// the rendered polygon's `points` attribute will be '10,10 50,10 50,50'
// can be obtained by `p.findView(paper).vel.findOne('polygon').attr('points');`</code></pre>
